In general, a compressor, which is an apparatus for converting mechanical energy into compressed energy of a compressive fluid, is used as a part of a freezing system, for example, a refrigerator and an air conditioner. Among the compressors, a reciprocating compressor sucks, compresses and discharges a refrigerant gas by linearly reciprocating an inner piston inside a cylinder. Driving types of the piston are divided into a recipro type and a linear type. A linear motor is used in the linear type.
As the linear motor itself directly generates a linear driving force, the linear compressor does not need a mechanical conversion system, simplifies the structure, and decreases an energy conversion loss. In addition, as a connection portion causing friction and abrasion does not exist, the linear compressor can considerably reduce noises. In the case that the linear compressor is employed in a refrigerator or an air conditioner, since a stroke voltage applied to the linear compressor can be changed to vary a compression ratio, the linear compressor can be used for a variable cooling control. However, in the case of the reciprocating compressor, particularly, in the case of the linear type, the piston reciprocates inside the cylinder in a state where it is not mechanically restricted. Accordingly, if an excessive voltage is abruptly applied, the piston runs against the cylinder wall, and if a load is large, the piston does not move forward, which results in abnormal compression. It is thus essential to control the piston to regulate the movement of the piston with regard to the variation of the load or the voltage.
FIG. 1 is a configuration view illustrating a conventional controlling apparatus for a linear compressor. The conventional controlling apparatus for the linear compressor includes a power unit 400 with a predetermined frequency for supplying AC power, a linear compressor 100 with a predetermined inductance L connected to the power unit 400 and provided with a coil wound motor, a sensor unit 500 for sensing a voltage and a current applied to the linear compressor 100, a microcomputer 600 for receiving a signal from the sensor unit 500 and outputting a control signal, a control unit 300 connected to the linear compressor 100, a capacitor 200 with a capacitance C connected in series to the linear compressor 100, a value (resonance frequency) obtained by multiplying the capacitance C by the inductance L of the linear compressor 100 being larger than the frequency of the power unit 400, and a switch unit 700 for bypassing the current flowing through the control unit 300 according to the control signal from the microcomputer 600.
When the microcomputer 600 judges a current condition as a normal condition in which a load variation is not serious, the microcomputer 600 applies the control signal to the control unit 300, so that input power passes therethrough. For this control, the capacitor 200 with the sufficiently small capacitance C must be used in the prior art.
FIG. 2 is a graph showing current and voltage waveforms in FIG. 1.
A stroke of the linear compressor 100 of FIG. 1 is controlled through a current phase control using the control unit 300 by controlling the switch unit 700. In this state, FIG. 2 shows phases of a current I and a voltage II applied to the linear compressor 100. As shown in FIG. 2, in the conventional controlling apparatus, the capacitor 200 with the sufficiently small capacitance C is connected in series to the linear compressor 100 and the control unit 300, so that the phase of the current I applied to the linear compressor 100 and the control unit 300 precedes the phase of the voltage II by a phase difference.
Due to the phase difference between the current I and the voltage II, when the microcomputer 600 sends an on driving signal to the control unit 300 when the voltage II is over 0 V, since the current I has been relatively reduced, a required driving force is not transferred to the linear compressor 100. As the phase of the current I precedes the phase of the voltage II, a necessary driving force is not generated. Moreover, such a phase difference lowers efficiency of the consumed power.